Interaction between sex-determining genes from two species: clues from hybrids.

Hybrids provide an interesting model to study the evolution of sex-determining genes and sex chromosome systems as they offer the opportunity to see how independently evolving sex-determining pathways interact . In this context, the genus represents a stimulating model, since species with non-homologous sex chromosomes and different sex-determining genes have been identified. In addition, the possibility of interspecies breeding is favoured in this group, which arose by alloploidization events, with species ploidy ranging from 2 = 2 = 20 in (the only diploid representative of the genus) to 2 = 12 = 108 in . To study how two sex-determining genes interact , × s hybrids were produced. Gonadal differentiation in these hybrids revealed that the gene is dominant over male-determining sex chromosomes (Y or Z), even though the Y chromosome is dominant in (Y > W>Z). In the absence of the gene (the Z chromosome from is present), the W chromosome from is able to trigger ovarian development. Testicular differentiation will take place in the absence of W chromosomes from any of the parental species. The dominance/recessivity relationships between these sex-determining loci in the context of either parental genome remains unknown. This article is part of the theme issue 'Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)'.